Modulatory effect of nitric oxide on acetylcholine-induced activation of cat petrosal ganglion neurons in vitro

The inhibitory effect of nitric oxide (NO) on carotid chemosensory response s to hypoxia has been attributed in part to an antidromic inhibition of che moreceptor cells activity. However, NO may also modulate the activity of th e primary sensory neurons because NO is produced in the soma of these neuro ns located in the petrosal ganglion. Since a population of petrosal neurons is selectively activated by acetylcholine (ACh), we studied the effects of NO-donor, sodium nitroprusside (SNP), and the NO-synthase inhibitor, Nw-ni tro-L-arginine methyl ester (L-NAME), On the responses evoked in the caroti d sinus nerve (CSN) by ACh applied to the petrosal ganglion in vitro. ACh ( 1 mu g-1 mg) increased the frequency of action potentials recorded from the CSN in a dose-dependent manner. SNP (10-50 mu M) reduced the sensibility a nd amplitude of the CSN response to ACh, although the maximal response appe ars less affected. The withdrawal of SNP from the superfusion medium increa sed the sensibility of the responses to ACh. L-NAME (1-2 mM) slightly incre ased the sensibility of the ACh-induced responses, effect that persisted af ter L-NAME withdrawal. These results suggest that NO may play a role as mod ulator in this autonomic primary sensory ganglion. (C) 1999 Elsevier Scienc e B.V. All rights reserved.